The invention relates to a variable valve timing mechanism for an internal combustion engine with at least one camshaft for operating exhaust valves and two camshafts rotating in opposite directions and actuating, by way of rocker arms, inlet valves which are spring biased in a closing direction, wherein one of the inlet valve camshafts controls the valve opening process and the other controls the valve closing process such that, by changing the relative rotation of the two inlet valve camshafts, the opening duration of the inlet valves can be controlled.
Such variable valve timing mechanisms are known for example from DE 42 44 550 A1, FIG. 5. In the arrangement shown therein, the angular position of the two intake camshafts relative to the crankshaft is adjustable by a special control mechanism. The angular position of one of the intake camshafts is adjustable by a phase control mechanism operating with the axial displacement of a transmission member which adjusts the angular position of the camshaft, whereas the control mechanism for the other camshaft includes a four-wheel coupler drive linkage. The two control mechanisms are adjustable by way of a common control member, that is, the coupler of the coupler linkage, such that they are adjustable in certain relationship with one another. This arrangement is relatively complicated and requires a high mechanical expenditure in order to realize the desired control accuracy. Still, inspite of the high mechanical expenditure, the adjustment possibilities are quite limited because the camshafts cannot be controlled independently.
It is the object of the present invention to provide better solution for a variable valve timing mechanism.